1. Field of the Invention
This invention relates to magnetic sensors of the spin-valve type using giant magnetoresistive elements (or GMR elements) and manufacturing methods therefor.
This application claims priority on Japanese Patent Application Nos. 2003-421236, 2003-199280, and 2003-199281, the contents of which are incorporated herein by reference.
2. Description of the Related Art
Conventionally, various types of magnetic sensors, which use spin-valve type magnetoresistive elements such as giant magnetoresistive elements (or GMR elements) whose resistances change when exposed to magnetic fields, have been developed and put into practical uses.
For example, a GMR element comprises a pinned layer whose magnetization direction is pinned in a prescribed direction and a free layer whose magnetization direction changes in response to an external magnetic field, wherein it presents a resistance responding to a relative relationship between the pinned layer and free layer in the magnetization direction, whereby it is possible to detect the external magnetic field by measuring the resistance thereof.
The GMR element included in the magnetic sensor is formed by fine line patterns, which are folded in a zigzag manner multiple times, whereby it is possible to increase the overall path length within a very small area and to thereby increase the impedance, by which it is possible to reduce an electric current being consumed.
In the aforementioned GMR element having zigzag patterns, folded portions (or bent portions) of fine lines are formed by magnetoresistive films, which may make the sensitivity direction of the GMR element non-uniform; in other words, this damages the linear relationship (or linearity) between the external magnetic field and the resistance of the magnetoresistive element; hence, it becomes difficult to accurately measure the intensity of the magnetic field.
In consideration of the aforementioned drawback, there has been developed a magnetic sensor using a GMR element having zigzag patterns in which the bent portions are formed by nonmagnetic films. Examples of conventionally-known magnetic sensors are disclosed in Japanese Patent Application Publication No. 2000-206217 and Japanese Patent Application Publication No. 2002-299728.
Compared with the magnetic sensor whose bent portions of GMR elements are constituted by magnetoresistive films, the aforementioned magnetic sensor can accurately measure the intensity of the magnetic field, whereas it may be insufficient for the aforementioned magnetic sensor to maintain the uniaxial anisotropy in the free layer of the magnetoresistive film due to the nonmagnetic films corresponding to the bent portions. For this reason, when a disturbance magnetic field having a relatively high intensity is applied to the magnetic field from the exterior, the magnetization direction of the free layer may not match (or restore) the initial magnetization direction thereof; thus, it may not be always possible for the magnetic sensor to measure the intensity of the external magnetic field with a good reproducibility.
In addition, there has been developed another magnetic sensor in which in order to maintain the uniaxial anisotropy in the free layer of the GMR element, a bias magnetic layer (corresponding to a permanent magnet film composed of a ferromagnetic substance) is arranged in contact with both ends of the magnetoresistive film in proximity to the bent portions of the GMR element.
In the aforementioned magnetic sensor, the GMR element having zigzag patterns is constituted by the magnetoresistive film and nonmagnetic film, wherein the permanent magnet film is arranged in proximity to the bent portions in the resistance circuitry thereof. That is, this magnetic sensor is very complicated in structure and is very difficult to manufacture.
FIG. 49 is a cross-sectional view diagrammatically showing the constitution of a conventionally-known magnetic sensor, which is disclosed in Japanese Patent Application Publication No. H12-137906, for example.
The magnetic sensor of FIG. 49 comprises a substrate 201 composed of a quartz or silicon wafer having a prescribed thickness, a magnetoresistive element 202 composed of a GMR element arranged on the substrate 201, an embedded film 203 composed of a nonmagnetic material arranged on the substrate 201, a bias magnetic layer 204 composed of a permanent magnet film, which is connected to both ends of the magnetoresistive element 202 and is arranged on the substrate 201 via the embedded film 203, a first protective film 205 composed of a silicon oxide film and a second protective film 206 composed of a silicon nitride film by which the overall surface of the magnetoresistive element 202 and the bias magnetic layer 204 is covered.
The first protective film 205 and the second protective film 206 can be collectively referred to as a protective film 207.
In the aforementioned magnetic sensor, the overall upper surface of the bias magnetic layer 204 is not entirely covered with the lower surface of the magnetoresistive element 202 at its both ends. For this reason, the magnetoresistive element 202 is connected in such a way that it overhangs a part of the upper surface of the bias magnetic layer 204. This magnetic sensor may cause a separation of the protective film 207 in the interface between the bias magnetic layer 204 and the protective film 207 during a heat-cool cycling test (or a thermal cycling test), for example. That is, it is demanded to provide a magnetic sensor having a sufficiently high degree of environmental durability.